The present invention relates to propylene copolymers. More particularly the invention relates to copolymers formed from the copolymerization of propylene and diene monomers and articles produced therefrom.
Polypropylene is an inexpensive thermoplastic polymer employed in a wide variety of applications, the articles of which include, for example, films, fibers, such as spunbonded and melt blown fibers, fabrics, such as nonwoven fabrics, and molded articles. The selection of polypropylene for any one particular application depends, in part, on the physical and mechanical properties of the polypropylene polymer candidate as well as the article fabrication mode or manufacturing process. Examples of physical properties include density, molecular weight, molecular weight distribution, melting temperature and crystallization temperature. Examples of mechanical properties include heat distortion temperature (HDT) and Flexural Modulus. Examples of factors relevant to the processing environment include the melt flow rate (MFR), cycle time, bubble stability, sag resistance, melt strength and shear/elongational viscosity.
In some instances articles formed from polypropylene, for example, via an injection molding process, may require a high degree of structural rigidity. This structural rigidity may be directly correlated with the value of modulus (e.g. flexural modulus), such that to achieve high structural rigidity in a molded article, polymers exhibiting high modulus values are desirable. Additionally, for such articles to be economically manufactured, the fabrication mode must be capable of producing the article at a selected rate, also referred to as xe2x80x9ccycle timexe2x80x9d. The cycle time for injection molding may generally be described as the duration from the introduction of molten polymer into the mold to the release of the molded article from the mold. The cycle time is a function of the viscosity of the molten polymer. Cycle time also relates to the crystallization temperature of the polymer. Generally, the crystallization temperature is the pivotal temperature at which the molten liquid polymer hardens. This hardening is due, in part, to the formation of crystalline structures within the polymer. It follows that as the molten polymer cools in the mold, molten polymers having higher crystallization temperatures will form crystalline structures sooner than polymers having lower crystallization temperatures. As such, shorter cycle times may be achieved by using polymers with higher crystallization temperatures. It will be understood from this that many variables may be relevant and require consideration before selecting a polymer for a particular application.
As the criteria for polymer applications and articles formed therefrom continue to evolve, there remains a need to continually modify and improve the physical, mechanical and rheological properties of polymers, and in particular polypropylene polymers, to meet these evolving criteria.
The present invention involves the reaction, and particularly a copolymerization reaction, of olefin monomers, wherein one such olefin monomer is desirably propylene, with an xcex1,xcfx89-diene and the olefin/xcex1,xcfx89-diene copolymers resulting form that reaction. Additionally, the present invention involves a copolymerization reaction of olefin monomers, wherein the reaction includes propylene and ethylene copolymerization with an xcex1,xcfx89-diene and the copolymers that are made. These copolymers may be employed in a variety of articles including include, for example, films, fibers, such as spunbonded and melt blown fibers, fabrics, such as nonwoven fabrics, and molded articles. More particularly, these articles include, for example, cast films, oriented films, injection molded articles, blow molded articles, foamed articles, foam laminates and thermoformed articles.
It should be noted that while linear xcex1,xcfx89-dienes are preferred, other dienes can also be employed to make polymers of this invention. These would include branched, substituted xcex1,xcfx89-dienes, such as 2-methyl-1,9-decadiene; cyclic dienes, such as vinylnorbornene; or aromatic types, such as divinyl benzene.
Embodiments of the present invention include copolymers having from 98 to 99.999 weight percent olefin units, and from 0.001 to 2.000 weight percent xcex1,xcfx89-diene units. Copolymer embodiments may have a weight average molecular weight from 50,000 to 2,000,000, crystallization temperatures from 115xc2x0 C. to 135xc2x0 C. and a melt flow rate (MFR) from 0.1 dg/min to 100 dg/min. Note that the invention polymers display these high crystallization temperatures intrinsically; there is no need for externally added nucleating agents. The copolymer may further include at least two crystalline populations. Some embodiments have melting point ranges for one crystalline population that are distinguishable from the melting point range of another crystalline population. The difference in melting point range can be from 1xc2x0 C. to 16xc2x0 C. This represents the difference between the melting points of the two crystalline populations. In other embodiments, one of the crystalline populations has a melting point from 152xc2x0 C. to 158xc2x0 C. and another crystalline population has a melting point from 142xc2x0 C. to 148xc2x0 C.
In other embodiments, the copolymer includes from 90 to 99.999 weight percent of propylene units, from 0.00 to 8 weight percent of olefin units other than propylene units and from 0.001 to 2.000 weight percent xcex1,xcfx89-diene units. Copolymer embodiments may have weight average molecular weights from 50,000 to 2,000,000, crystallization temperatures (without the addition of external nucleating agents) from 115xc2x0 C. to 135xc2x0 C. and MFRs from 0.1 dg/min to 100 dg/min. The olefin may be any of C2-C20 xcex1-olefins, diolefins (with one internal olefin) and their mixtures thereof. More specifically, olefins include ethylene, butene-1, pentene-1, hexene-1, heptene-1,4-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-hexene, 5-methyl-1-hexene, 1-octene, 1-decene, 1-undecene, and 1-dodecene. The copolymer may further include at least two crystalline populations. These embodiments have melting point ranges for one of the crystalline populations that are distinguishable from the melting point range of another crystalline population by a temperature range of from 1xc2x0 C. to 16xc2x0 C. More desirably, one of the crystalline populations has a melting point in the range from 152xc2x0 C. to 158xc2x0 C. and another crystalline population has a melting point in the range from 142xc2x0 C. to 148xc2x0 C.